I've noticed sometimes that threads that I am subscribed to seem to have an "re:" prepended to the subject line every time a reply to that thread is posted, even if there is already an "re:" in the subject line.
Like this one:http://fudforum.org/forum/index.php?t=rview&goto=183204

Is that someone's email client doing that, or is it something FUDforum is doing?
Either way, isn't there something we can do about that?

I will be connected my FUDforum forums to some external mailing lists I don't manage, so I'm very sensitive to how email from my forum looks.

It happens on multilingual forums. For example, an English theme will look for and remove 'Re:', but French forums use 'Re :' (note the extra space), and won't be bothered with 'Re:'. When you mix the two in one forum (like here), you get strange combinations of "Re: Re :". Throw in a bit of German, and you may get "Re: Re : Aw:", etc.